The present invention relates in general to apparatus and methods for stacking generally flat objects, including but not limited to magazines, newspapers, and the like; and the invention relates more particularly to stacking apparatus that is adapted to stack magazines or the like that have labels thereon according to the postal zip codes on the labels, so that all labels in each stack of magazines or the like will be of the same zip code.
Automatic labeling machines for applying computer prepared labels to magazines or the like have been available for some time that are capable of labeling up to about 30,000 magazines per hour. For example, a labeling machine that is particularly suitable for feeding stacking apparatus of the present invention is a Xerox Cheshire 528 labeler, which is capable of applying labels to magazines or the like at a rate of about 27,000 per hour.
However, prior art stacking machines adaptable for "in-line" cooperation with such high speed labeling machines and capable of stacking according to zip-coded labeling, have not been capable of handling such capacity. The applicant is aware of only two prior art types of commercial stackers capable of handling zip-coded stacking. One of these is the "shuttle lock-out" approach, wherein the labeling machine is stopped for each zip code change. This cuts the maximum production rate to only about 60% of the potential labeler production rate. Thus, for a maximum labeling rate of about 27,000 per hour, the zip code stacking cuts the maximum possible rate to approximately 16,000 per hour, and this is further reduced to about 13,000 per hour figuring the typical down-time of about 20%.
The second prior art type of commercial stacker of which the applicant is aware that is capable of handling zip code stacking is the "interceptor plate" type, wherein each zip code is stacked on a "false shelf" interceptor plate. When a zip code has stacked, up to a maximum of about 8 inches thick, the plate cycles out and back in between adjacent magazines of different zip codes. This involves the plate shifting out of the way, the stack falling about 9 inches, and the plate than shifting back into position to catch the very next magazine, which starts the next zip code stack. This approach requires that the labeler be slowed down to approximately 14,000 per hour to accommodate the stacker speed limitation of about 15,000 to 16,000 per hour. With any greater speed of operation of the stacker, the plate starts coming back too soon and hitting the stack. With the typical 20% down time, the 14,000 per hour capability of this type stacker is reduced to a net of about 11,000 per hour.
It will thus be seen that much of the capacity of conventional labeling machines could not heretofore be utilized with zip coded labeling because of the inadequacy of available zip code stackers.
Another problem in connection with such zip code stackers was the manner in which shift registration was accomplished. The first label in each zip code was suitably marked so as to be registered by an optical reader associated with the labeling machine, and the resulting signal was required to be delayed the entire length of time for the corresponding label and its associated magazine to be fed to the stacker. In the aforesaid shuttle lock-out type of stacker, this involves a two-label magazine cycle delay in the signal before its operational application; while in the aforesaid interceptor plate type of stacker this involved the use of a minicomputer to provide about a 40-label magazine cycle delay of the signal before its application. These extended time delays between the reading and the application of the shift signal introduced undesirable complexities into the prior art apparatus, with resulting loss in reliability.
A third type of prior art stacker is the "rotary indexing" type stacker, wherein a big wheel having a series of peripheral compartments is indexed to successive compartments for receiving successive stacks in the compartments, usually stacks of the same numbers of magazines or the like, as for example 25 magazines in each stack. The rotary indexing type stacker is quite slow in operation, and is not suitable for zip code stacking.